1. Field of Invention
This invention relates to systems and methods for optimally rotating high addressability images. More specifically, this invention relates to systems and methods for rotating of high addressability binary images by clustering the high addressability image to form multi-bit pixels, determining neighborhood information of the multi-bit pixels in the image, and rotating while minimizing the presence of false contours, maintaining edge integrity, maintaining the density, and not introducing undesirable textures into the rotated image.
2. Description of Related Art
The digital reproduction, transfer or display of various images presently occurs using a variety of devices and systems in a variety of environments. The image may be input into a device, processed in some manner, and then output from the device, for example. In some applications, it may be necessary or desirable to convert the image between the input and the output of one device for the specific purpose of using the converted image data by another device. In other applications, it may be necessary or desirable to convert the input image for some particular application within a device itself.
The pixels in a binary image may be either on or off, i.e., black(1) or white(0), respectively. In particular, the binary image may be a high addressability binary image. A high addressability binary image is an image created by a device such that the spatial addressability of the writing spot is finer than the size of the writing spot. High addressability also often refers to an addressability resolution, in a first direction, that is finer than the spatial addressability resolution in a second direction that is, for example, perpendicular to the first direction. High addressability data can be used to render edges in text and line art regions at a high spatial precision in the high addressability direction. High addressability data can also be used in halftone regions to provide additional spatial resolution in the high addressability direction.
Illustratively, FIG. 1 is a diagram showing a high addressability pixel grid. As shown in FIG. 1, the spatial addressability of the pixels in the horizontal direction, i.e., the fast scan direction, is finer than in the vertical direction, i.e., the slow scan or process direction. For a laser raster output scanner, the fast scan direction is the direction in which a laser beam of a printer, for example, sweeps to print an image on a recording medium. The recording medium may be a xerographic photoreceptor that will develop and transfer an image onto a sheet of paper, for example. The photoreceptor is advanced in a direction perpendicular to the fast scan direction, i.e., the slow scan or process direction. The photoreceptor may be advanced using rollers for a belt-type device, or the photoreceptor may be a rotating drum, as is commonly used in a printer, for example. It should be recognized that other writing devices may also have high addressability capability, such as an LED image bar writer. In these other devices, the orientation of the grids may be rotated, for example.
FIG. 1 shows the size of a nominal pixel and a high addressable pixel, as well as the size of a writing spot. The addressability in the fast scan direction is controlled by a laser beam modulator, for example. The addressability in the slow scan or process direction is controlled by the photoreceptor advance mechanism of the printer or copier. The laser beam is capable of modulation to a resolution of the high addressable pixel. However, the photoreceptor advance mechanism is not capable of such fine resolution. Rather, the paper feed mechanism is only capable of a nominal pixel resolution.
Various methods for image processing are known. These methods may encompass processing using scanning, or other image acquisition, in conjunction with printing or displaying the image. Illustratively, high addressability methods conventionally typically involve modulating a writing member, such as a laser beam, at spatial increments finer than the size of the writing spot. Using high addressability imaging and modulation allows a particular device's spatial resolution to be improved or increased without actually increasing the number of pixels or dots per unit area in the input image data.
Accordingly, high addressability techniques use modulation to increase printer spatial resolution without modifying the physical printer device. As described above, high addressability techniques may be used to affect the horizontal spatial resolution. For example, doubling the printer modulation rate results in doubling the horizontal spatial resolution, while the vertical spatial resolution remains unchanged.